How You Get Mono — Plus Everything You Should Know About Avoiding Infection

Mono is most commonly caused by the Epstein-Barr virus, which spreads via saliva.

Scott Kleinman/Getty Images

Infectious mononucleosis (more commonly known as mono) is a disease you can catch if you get infected with certain viruses, mainly the Epstein-Barr virus (EBV).

“Ninety percent of cases of infectious mononucleosis are caused by Epstein-Barr virus,” says Stan Deresinski, MD, a clinical professor in medicine at Stanford University in California, who specializes in infectious diseases. “The range and severity of the signs and symptoms can be variable. And some infections with EBV are asymptomatic, particularly during childhood.”

Most Cases of Mono Are Caused by EBV Infection, Which Gets Passed via Saliva

If you do come down with mono after an EBV infection, symptoms tend to show up four to six weeks after you’re infected with the virus. (1) Even though the virus is not extremely contagious, it can spread among groups of people even if someone is not experiencing mono symptoms. EBV transmission occurs most often through saliva (why mono is also called the kissing disease), by: (2)

Sharing drinks or food

Sharing eating utensils, cups, or toothbrushes

Kissing

Having mouth contact with toys that have been drooled on by other children

Less common ways EBV is spread is through:

Sexual contact

Blood transfusions

Organ transplants

EBV is a very common virus, estimated to infect more than 95 percent of the world’s population at some point. (3) But, of course, not everyone who gets infected with EBV gets mono. About one-quarter of those infected with EBV get mono. (1)

When EBV infects young children, there are often no symptoms. Sometimes children have a mild illness that may be mistaken for a mild cold or flu that goes away on its own. (2,4) Conversely, EBV tends to cause more severe illness in people who don’t catch EBV until later adolescence or adulthood. (4)

It isn’t entirely known why adolescents are made so much sicker from initial EBV infection than young children. It may be that the stronger immune response to EBV from a more mature immune system may be partly to blame. (4)

Other research suggests that most people are infected with EBV early in life, when it doesn’t cause mono or other problems — which would explain why the infection is so prevalent, but mono is not, according to the National Institutes of Health. (5)

EBV does not occur in epidemics. (4)

EBV Can Cause Other Diseases, Too — Including Some Cancers

EBV infects humans and a few other primate species. (6) It is one of the group of viruses known as human herpesviruses. Specifically, EBV is human herpesvirus 4. (2) Oral and genital herpes are caused by the herpesviruses 1 and 2. Chickenpox and shingles are caused by the human herpesvirus 3, and there are other human herpesviruses that also cause disease.

Dr. Deresinski explained, “All herpes viruses establish latency, a state of relative dormancy, within infected cells. The mechanisms by which this occurs remain incompletely understood.”

Like other human herpesvirus infections, EBV can remain latent for the life of the person. EBV can also reactivate, and it is sometimes infectious to others, even if the person with the reactivated virus does not show symptoms. (6)

Most people can get mononucleosis from EBV only once. (6,7) If the virus reactivates, it usually does not cause mono symptoms to reactivate.

There has long been a suspected link between EBV and some autoimmune diseases, and a study published in April 2018 in the journal Nature Genetics identified various genes associated with those autoimmune diseases that bind with EBV proteins, offering some pretty convincing evidence that EBV plays a role in those chronic problems — including lupus, multiple sclerosis (MS), type 1 diabetes, juvenile idiopathic arthritis, and celiac disease. (8)

EBV has also been linked to Hodgkin lymphoma, non-Hodgkin lymphoma, and Burkitt's lymphoma. This has been reported in Africa, alongside malaria infections. (6)

Additionally, EBV infection has been reported to cause chronic active EBV infection (CAEBV) in rare cases. (4) Someone with CAEBV has symptoms of mono-like fever, lymph node swelling, and liver and spleen swelling for a prolonged period of time.

Some people have speculated about a link between chronic fatigue syndrome and EBV, but this link has yet to be proven. (4)

Other Germs Besides EBV Can Cause Mono

Other germs can also cause the symptoms of mononucleosis.

Approximately 10 percent of mononucleosis-like cases are not caused by EBV. (4)

If Epstein-Barr virus (EBV) is ruled out as a cause of symptoms, providers may want to make sure that you are not showing symptoms of infection from other microbes. Among the 10 percent of infectious mono cases not caused by EBV, Deresinski says that the most common is cytomegalovirus (CMV). Doctors may also check for toxoplasmosis, human herpes viruses 6 and 7, HIV infection, rubella, viral hepatitis (hepatitis A, B, or C), or adenovirus. (2)

Can Mono Be Prevented?

Although attempts are being made to develop a vaccine against Epstein-Barr virus, none have yet been approved. (3,6) Researchers suggest that an EBV vaccine would need to be administered before the age of 12 to be helpful in the United States. (3)

Currently to avoid getting mono doctors recommend you:

Not share drinks, food, or personal items with people who have mono

Not kiss or have sex with people who have mono

Sign up for our Sexual Health Newsletter!

Thanks for signing up for our newsletter! You should see it in your inbox very soon.

Editorial Sources and Fact-Checking

Balfour HH Jr., Sifakis F, Sliman JA, et al. Age-Specific Prevalence of Epstein-Barr Virus Infection Among Individuals Aged 6-19 years in the United States and Factors Affecting Its Acquisition. The Journal of Infectious Diseases. October 15, 2013.